1. Field of the Invention
This invention relates to an integrated patient simulator and methods of using the same. In particular, this invention discloses an improved patient simulator capable of realistically simulating nerve stimulation, lung movement, lung volume measurement and lung breathing noise, administration, detection, identification and quantification of medicaments and fluids introduced during simulated surgery, bronchial resistance, computer controllable compliances and also possessing an improved computational configuration, an electric cardiac synchronization pulse, audible heart and lung sounds, simulation of continuous blood gases, pulmonary artery (PA) catheter inflation detection, difficult airway, spontaneous breathing and other anesthesiological indications, and gas exchange via a mass-flow controller.
2. Background of the Invention
Currently, a new resident in medicine will receive a very limited duration of didactic teaching about the principles of particular medical procedure, such as anesthesia, before delivering care to his/her first real patient. The resident is then faced with a new and unfamiliar environment while shouldering the tremendous responsibility of caring for an ill and sometimes anesthetized patient. Similarly, experienced physicians who require continuing medical education, refresher courses (e.g., handling of rare ailments and situations) or familiarization with newly introduced and/or technologically sophisticated equipment or procedures do not have the opportunity for hands-on practice in a realistic environment, without risk to a patient. Of course, these undesirable situations also apply to other disciplines such as allied health care and veterinary medicine, for instance.
The patient simulator disclosed in U.S. patent application Ser. No. 07/882,467 addresses the above-mentioned deficiencies in medical, allied health care and veterinary education. The improved self-regulating full-scale patient simulator technology described herein comprises further embodiments of a patient simulator.
The lung portion of the integrated patient simulator disclosed herein consumes and/or produces gases including oxygen, carbon dioxide, nitrogen, nitrous oxide and volatile anesthetics. Under the control of a mathematical model of human physiology implemented on a computer, uptake and delivery of the above mentioned gases is computed by the uptake and delivery module of the physiological model. The computed uptake and delivery is then physically created by gas substitution in the hardware module for simulating gas exchange in the lung simulator portion of the patient simulator. The lung will also simulate spontaneous inspiration with computer control of tidal volume (VT), respiratory rate (RR) and functional residual capacity (FRC) and will also allow the simulation of a cough. In addition, the lung will exhibit the desired lung mechanics and gas exchange when mechanically or manually ventilated.
The patient simulator system of this invention has several components including lung mechanics (software and hardware); gas exchange (software and hardware); a physiologic model (software); cardiovascular; uptake and distribution; neuromuscular system; pharmacokinetics/pharmacodynamics; physiologic control models; and a unique linking of the different subsystems of the patient simulator so that the patient responds realistically to inputs from the trainee/student.
A major improvement of the lung/patient simulator is that it allows realistic action/reaction interplay between the actions of the trainee, responses of the simulated patient, data shown on the monitors and subsequent actions by the trainee. Another significant improvement that distinguishes the lung/patient simulator from similar systems is that its software and hardware are self-regulating. The present hybrid (mechanical and mathematical) lung model regulates itself regardless of type of gas (air, anesthetics, hypoxic, etc.) inhaled, and, surprisingly, even the blunting of physiological control mechanisms (e,g., ventilatory response to carbon dioxide) is self-regulated.
The present patient simulator is an integrated, self-regulating system. For instance, in a non-self-regulating system, an awkward input situation would invariably lead to physiologically implausible behavior from the system or such stimuli would result in an inability of the system to handle the input at all. A self-regulating system is more robust in the accommodation and simulation of unplanned events because it will still provide an appropriate response. Thus, self-regulation is highly desirable, yet glaringly absent from the prior art.
For instance, if the trainee accidently ventilates the lung with a hypoxic (lacking oxygen) gas mixture (e.g. pure argon gas), a conventional system may not be able to react appropriately. However, the present invention provides an integration of relevant systems such that, through self-regulation, appropriate simulated manifestations of hypoxia would be produced in the various output devices of the patient simulator, e.g. increased breathing rate and heart rate.
As another example, those skilled in the art are aware that increased CO.sub.2 levels in the lung will cause hyperventilation. Hyperventilation results in lowering of CO.sub.2 levels in the lungs due to washing away of the carbon dioxide. In a non-self-regulating patient simulator, increased lung CO.sub.2 may or may not lead to increased ventilation. If no increase occurs, the reality of the simulation is decreased, thereby lessening the teaching value of the simulation.
Thus, it is clear that self-regulating systems hold clear advantages above non-self-regulating systems.
Furthermore, a means for adequately handling the injection of liquid anesthetic into the breathing circuit has been attempted by other researchers. The problems encountered in the prior art included (a) freezing of the location where the liquid anesthetic is introduced because of the heat of vaporization extracted from the surroundings as the liquid anesthetic evaporates, (b) pooling of the injected liquid through lack of heat to vaporize the liquid anesthetic and (c) uncontrolled evaporation of the anesthetic liquid from the syringe to the breathing circuit (i.e. the tubing or conduit assembly which physically connects the anesthesia machine or ventilator to the patient/manikin). The instant integrated patient simulator solves these problems by providing a means as usable not only in the simulation but in real life anesthesia applications.
A real life practitioner must be able to react to a patient who is undergoing a degree of bronchial restriction. Therefore, it is highly desirable for a patient simulator to be able to simulate bronchial resistance where the restriction of gas flow may be varied upon a continuum. Without manual intervention, such capability is lacking in the prior art systems.
In a full-scale patient simulator, it is necessary to be able to simulate changes in bronchial resistance. In a full-scale simulator using real gas flows, independent computer-controlled variable orifices (with maximum openings of 0.5" diameter) placed in the bronchi would allow simulation of changes in bronchial or airway resistance. No prior art devices (e.g., photographic camera iris diaphragms) were found which could simulate variable bronchial resistances in the relevant diameter range. Furthermore, a device capable of allowing a suction catheter to pass down the bronchus was preferable. Thus, the present invention could not use butterfly valves with an internal diameter of 0.5".
Another possible embodiment was a stepper motor actuated cam or lever that presses a flexible conduit closed. However, because the stepper motor would have needed to be overly large in order to provide the force necessary to maintain the flow area completely closed and capable of holding a pressure of 120 cm H.sub.2 O, one of the design specifications, it was highly desirable and necessary to design an alternative computer-controlled variable orifice device.
During simulation, it is preferable if the drugs and IV fluid administered by the trainee to the simulated patient are automatically sensed and input into the computer, rather than having to depend on the simulation instructor to recognize and manually enter the drug or IV fluid type, concentration and dose administered to the patient. Thus, in prior systems, the simulation instructor might be distracted and miss the administration of the drug or IV fluid by the student or might manually enter into the simulation controller the wrong type, concentration or dose of the drug or IV fluid.
In addition, the amount of drug and/or IV fluid administered by the student is a critical input to the physiological model of the patient because the response of the patient is dose- and volume-dependent. The amount of IV fluid dripped into the patient is also a parameter that needs to be quantified if the fluid balance of the simulated patient is to be correctly modelled. It does not appear that prior art systems have contemplated a means for quantification of drug administered. As in drug identification, a system that will allow quantification of the amount of drug or IV fluid injected via an intravenous (IV) line without the need for a human observer is highly desirable.
U.S. patent application Ser. No. 07/882,467 disclosed and claimed one embodiment of distributed processing network for implementing the computer portions of the current patient simulator: a ring-shaped array of single-board computers (i.e., DACS PAN-Data Acquisition and Control System).
It has been found that a star configuration for a network of single board computers is more preferable. The extent of computational power and parallel processing required for simulating a patient's different physiological subsystems is facilitated by a distributed processing network. For example, one computer takes modulates the mechanical lung while another controls the palpable pulses. The ring network is less robust than a star network configuration because if one of the single board computers becomes non-functional, the entire network ceases to operate. In the star network configuration, the network will still function even if one of the computers on the network fails.
The realism of a simulation would be marred if the different signs or variables dependent on the cardiac rhythm were at different frequencies (e.g., an ECG heart rate of 70 beats per minute (bpm) but a pulse rate from the pulse oximeter of 90 bpm). A mechanism that allows synchronization of all cardiac related events is, therefore, highly desirable and necessary for a realistic patient simulator.
The realism of a patient simulator would also be compromised if the simulator lacked audible heart, lung and breathing sounds emanating from the appropriate portions of the simulator. In addition, spontaneous breathing is highly desirable and adds to the realism of the patient simulator.
In addition, a realistic patient simulator should be able to simulate the monitoring of continuous blood gases. Simulation of continuous blood gases monitoring is highly desirable in light of recent technological advances implementing such technology in the everyday practice of specialists. Furthermore, it is highly desirable that a patient simulator have a means for detecting pulmonary artery (PA) catheter inflation.
Also, it is desirable to have a patient simulator capable of simulating a difficult airway. Difficult airway may be caused by a number of factors, such as an allergic reaction. In a difficult airway situation, the patient's trachea closes and prevents the flow of air in and out of the patient's lungs. Thus blocked, it is not possible to insert through the trachea an endotracheal tube (ETT) for securing the airway. It is highly desirable to provide a patient simulator capable of simulating this potential complication so that a trainee may be taught the proper response techniques such as a cricothyrotomy.
In addition, a difficult airway is a potentially lethal incident which anesthesiologists and other practitioners will likely encounter in actual patients. The American Society of Anesthesiologists has declared that is essential for any anesthesiologist to know how to handle such a situation as one of his or her practice parameters. Thus, the patient simulator provides a risk-free way to assess whether a trainee has successfully learned how to handle a difficult airway.
It is also desirable to provide a patient simulator capable of efficient and realistic gas exchange. Although a previous embodiment of the patient simulator contained a gas exchange module, the current module differs in important ways. Most importantly, the patient simulator disclosed herein uses mass flow controllers instead of frequency modulated valves as in the previous embodiment. Modulated valves provided inaccurate control over the flow rate of the different gases. In addition, maximum flow rate was limited in the prior embodiment in an unrealistic fashion which resulted in an unrealistically small difference between inhaled and exhaled oxygen levels. Finally, the frequency modulated valves resulted in inconsistent signals transmitted to the capnogram (depiction of CO.sub.2 level over time) which manifested themselves as ripples instead of straight lines, especially during plateau portions of the exhalation.
In addition, instead of a "copper kettle" Vernitrol vaporizer being used to introduce vaporized volatile anesthetic into the lung bellows, a syringe pump with a novel copper device is used in the present invention. In copper kettle systems, a carrier gas (generally O.sub.2) is bubbled through a pool of liquid anesthetic contained in a solid copper vaporizer. The use of the syringe pump eliminates the necessity of using a carrier gas per se thus simplifying the behavior of the gas exchange subsystem in general.
Realistic simulation of gas exchange is necessary because it allows the use of real or modified medical gas analyzers such as those used in real operating rooms. Other simulators do not model gas exchange at all. Instead, other simulators in the art bleed CO.sub.2 at variable rates into the bellows representing the simulated lungs. Thus, the simulators are incapable of simulating even the most rudimentary gases being exchanged such as oxygen. Nor are those systems capable of simulating the consumption or excretion of the amount of volatile anesthetics.
In addition, when an oxygen analyzer is used to sample the flow of gases into and out of a real patient's lung, exhaled oxygen will be notably lower than inhaled oxygen due to consumption in the patient's lungs. Unlike other simulators, the patient simulator of this invention is capable of realistically portraying to external monitoring equipment the differential between inspired and expired oxygen concentration. When other simulators are linked to an oxygen analyzer, the insiparatory and expiratory oxygen levels will be identical either indicating grave health problems to the patient or a serious breakdown in the realism of the simulation. Thus, the accurate modeling of gas exchange, as accomplished by the instant invention is highly desirable.